Development of thermoplastic vulcanizates based on in situ synthesized thermoplastic polyurethane and acrylonitrile-butadiene rubber: the influence of the curing system

Abstract

We prepared different thermoplastic elastomers (TPEs) using an internal mixer. We investigated the properties of thermoplastic polyurethanes (TPUs) produced from prepolymers with various isocyanate content and two different chain extenders to select the most appropriate TPU matrix for preparing thermoplastic vulcanizates (TPVs). Based on the results, we selected a prepolymer with moderate isocyanate content (10%) and the more flexible 1,6-hexanediol as a chain extender and prepared TPVs by dynamic vulcanization with in situ produced TPU. The rubber phase was acrylonitrile-butadiene rubber (NBR) with peroxidic and sulfuric curing with different accelerators. Dynamical mechanical analysis (DMA) results show that the room temperature storage modulus of the TPVs decreases due to the rubber phase. The TPU/NBR-CBS TPV with delayed action accelerator yields the highest tensile and tear strength and elongation at break. TPU/NBR-DCP made with a peroxide-based rubber blend shows similar tensile strength with significantly lower elongation at break and tear strength. The good mechanical properties of TPU/NBR-CBS can be explained by the long induction period, which allowed the rubber phase to disperse before vulcanization took place. In the TPU/NBR-DCP, the peroxide formed bonds not only in the rubber phase but also between the rubber and TPU phases, which is manifested in the high mixing torque and the result of the thermogravimetric analysis (TGA).